1. Field of the Invention
The present invention is directed to a hinge, and more particularly, a hinge having geared hinge members.
2. Description of the Related Art
As described in U.S. Pat. No. 3,092,870, one type of hinge, often referred to as a "gear hinge" includes a pair of hinge members having intermeshing gear portions. Applications for gear hinges include commercial swinging doors and commercial folding curtains used to divide large rooms. Such vertical applications typically require the hinge to extend the full length of the door or curtain and to have a plurality of thrust bearings distributed over the length of the hinge to support the weight of the hinge members. The thrust bearings are usually disposed in adjoining recesses of each hinge member.
One of the major problems associated with vertical applications of such full-length gear hinge is premature wear of the thrust bearings. Thrust bearing wear is often the result of twisting of the bearings as they transfer a load from one hinge member to the other. Additionally, wear may be caused by friction between the bearing and the hinge members. Because many thrust bearings are composed of relatively soft plastic, the likelihood that the thrust bearing may be twisted or damaged by friction between the bearing and the hinge is enhanced. Additionally, many bearings are produced by a conventional liquid molding process which causes the bearing to shrink at different rates at the bearing center as compared to the longitudinal end portions of the bearing. Thus, a 10% error factor must often be allowed for at the longitudinal end portions in order to assure proper clearance at the center. The 10% error at the end portions can result in a looser fit can contribute to twisting of the bearing and premature wear. Finally, wear may be caused by the sharp teeth of the gears rubbing against the bearing as the hinge rotates.
In addition to the cost of the thrust bearings themselves, replacement of the bearings typically requires that the door be taken down and that the hinge be disassembled. Thus, replacement of the bearings often requires considerable time, effort and expense.
U.S. Pat. No. 4,999,878 to Baer entitled "Thrust Bearing Assembly in a Pinless Hinge Structure" suggests reducing twisting of the bearings by increasing the length of the thrust bearings. This is said to be accomplished by essentially joining three smaller bearings in a spaced relationship. The three smaller bearings are positioned in three corresponding slots. Due to limitations in manufacturing tolerances, however, the bearings often may not fit properly into the corresponding slots such that only one of the bearings will actually rest upon the bottom of its respective slot. As a result, only a small single bearing may actually support the entire load, which can cause excessive twisting and premature wear.
U.S. Pat. No. 4,976,008 to Baer entitled "Multi-Piece Thrust Bearing Assembly for a Hinge Structure" proposes a hinge design which utilizes inserts, located between the thrust bearing and the hinge member, for protecting the bearing. Such a design appears to be relatively complicated and as a result subject to increased manufacturing and installation costs.
An additional proposed solution is described in U.S. Pat. No. 4,996,739 to Baer entitled "Thrust Bearing Assembly For Hinge Structure". The '739 patent in essence concedes that the thrust bearings will have to be replaced often and provides a relatively complicated multi-piece bearing that is designed to facilitate replacement.
Another problem often encountered can result from even a minor misalignment of the gears. If the gears of the hinge are misaligned, the sharp portions of a tooth of one of the gears will often grab an adjacent portion of a tooth of the other gear and bind. This binding usually results in a jerking movement as the gears rotate. Prior attempts to solve this problem have typically included machining the gears within extremely tight tolerances. Such machining can significantly increase the cost of the hinge.